1. Field of the Invention
The present invention relates to a tool holder that reliably secures a tool along a main shaft of a machine tool.
2. Description of the Related Art
Conventionally a tool holder is attached to the end of a main shaft to support a tool. This type of attachment is used in various machine tools including drill presses, milling machines, and machining centers.
With conventional tool holders, a main shaft rotates the tool to perform machining on a workpiece. Since the tool holder is removably attached to the main shaft, the main shaft is equipped with a retraction mechanism to draw in and secure a shank of the tool holder.
Conventional tool holders include a tool support section for attaching a tool, a shank including a tapered outer perimeter surface, a pull stud secured to the shank, and a flange having a larger diameter than the tapered hole.
Conventionally, the retraction mechanism pulls in the tool holder and fits and secures the shank to the tapered hole of the main shaft.
Unfortunately, high machining precision, of 1 micron error or less, is demanded from recent machining tools. During use, machining tools must operate while rotating the main shaft at high speeds of 30,000-40,000 rpm.
Consequently, the tool holder and the main shaft (rotating at high speeds) undergo undesirable rotary vibrations, which are a factor in degrading machining precision.
To minimize precision loss, it is desirable to increase securing strength by tightly securing the entire shank of the tool holder against the tapered hole of the main shaft. Unfortunately, due to machining tolerances in the tapered hole of the main shaft and the tool holder, the tool can heat up during use, resulting in detrimental thermal expansion of both the main shaft and the tool holder. Detrimental thermal expansion makes it impossible to secure the entire shank of the tool holder firmly and tightly against the tapered hole of the main shaft.
It is also impossible to abut the flange of the tool holder tightly to the end surface of the main shaft while having the shank of the tool holder tightly secured in the tapered hole of the main shaft. Consequently, conventional tool holders are not designed to abut the end surface of the main shaft.
Japanese laid-open patent publication number 8-108302 discloses a tool holder which includes a main holder unit having a shank and a flange. A sleeve is outwardly fitted to the shank so that it can move along an axial direction relative to the shank. The sleeve also has an outer perimeter surface with the same tapered shape as the tapered hole of the shank. An elastic member is interposed between the flange and the sleeve.
The sleeve is divided at one section along the perimeter, with the elastic body mounted in the resulting gap. When the retraction mechanism draws in the tool holder, the flange abuts the end surface of the main shaft. The sleeve is elastically pressed by the elastic member toward the base end of the main shaft. The sleeve is narrowed and engages the tapered hole and couples with the shank.
Japanese laid-open patent publication number 9-248727 discloses a tool holder, formed as described above, but instead of the sleeve with a division at one section, a sleeve with an inner groove at one section along the perimeter is used. With both above-described tool holders, the overall sleeve diameter is narrowed when the retraction mechanism pulls in the tool holder. As a result of this narrowing, the tapered outer perimeter surface of the sleeve cannot be tightly fitted and secured against the tapered hole. This makes it difficult to have a uniform contact force over the entire perimeter and provide secure coupling with the inner surface of the tapered hole. As a further detriment to this design, an increased number of parts is required and the structure is correspondingly complex, thus increasing manufacturing costs.
In a tool holder presented in Japanese laid-open patent publication number 7-96437, a ring-shaped groove is formed at the boundary between the shank and the flange. The ring-shaped groove allows a section of the flange to have a reduced thickness. When the tool holder is drawn in by the retraction mechanism, the flange abuts the end surface of the main shaft and is elastically deformed slightly, and acts as a disc spring. This mechanism engages the shank and the tapered hole. Unfortunately, the structure of the shank is the same as previous conventional shank structures, and roughly the same problems therefore exist as in conventional tool holders.
It is an object of the present invention to provide a tool holder which overcomes the drawbacks of the related art noted above.
It is another object of the present invention to provide a tool holder which provides both a firm and elastic fit of an entire shank in a tapered hole of a main shaft.
It is another object of the present invention to provide a tool holder which allows a flange to elastically abut an outer end surface of a main shaft.
It is another object of the present invention to provide a tool holder which prevents vibrations, greatly increases stability, and prevents loosening during use.
The present invention relates to a tool holder including a plurality of elastic engagement pieces arrayed along an outer perimeter of a shank. During and after assembly, the elastic engagement pieces elastically abut at least an inner surface of a tapered hole in a main shaft joined to the tool holder and deform slightly in a radial direction. The elastic engagement pieces provide uniform engagement force with the main shaft over a broad surface area. An elastic flange provides additional elastic engagement and easy separation from the main shaft. Together, the elastic engagement pieces and elastic flange reliably engage and securely attach the main shaft to the tool holder while aiding disengagement.
According to an embodiment of the present invention there is provided a tool holder apparatus, for securing a tool support section on a tool to a main shaft of a machining tool, comprising: at least a shank on the tool support section, the main shaft including a tapered hole, means for elastically securing the shank in the tapered hole of the main shaft and eliminating vibration and attachment failure during a use of the machining tool, a plurality of elastic engagement pieces in the means for removably securing, the elastic engagement pieces arrayed concentrically around an outer perimeter section of the shank, the elastic engagement pieces extending away from the shank and elastically abutting an inner surface of the tapered hole during an insertion of the shank into the tapered hole, and the elastic engagement pieces elastically deforming in a radial direction during the insertion, whereby the means for removably securing enables the elastic engagement pieces to absorb a plurality of use vibrations while maintaining a secure attachment to the main shaft.
According to another embodiment of the present invention there is provided a tool holder apparatus, further comprising: a plurality of ring-shaped grooves on an outer perimeter section of the shank, the plurality of ring-shaped grooves arrayed alternatingly with the plurality of elastic engagement pieces in an axial direction along the outer perimeter of the shank, the plurality of ring-shaped grooves being smooth radius contours, thereby minimizing elastic stress concentration, and the plurality of elastic engagement pieces extending integrally from shank, thereby simplifying manufacturing and assembly of the tool holder.
According to another embodiment of the present invention there is provided a tool holder apparatus, wherein: the plurality of ring-shaped grooves being positioned along the axial direction at a first diameter parallel to a central axis of the shank, the plurality of elastic engagement pieces each being a first length extending from each the respective ring-shaped groove to a sloped inner surface of the tapered hole, ends of each the elastic engagement piece arrayed in a plane parallel to the sloped inner surface, whereby each the elastic engagement piece contacts the sloped inner surface simultaneously during the insertion to provide easy alignment and tight attachment, and the first length of each the elastic engagement piece being dependant upon a position on the shank relative to the sloped inner surface, whereby the first length of the elastic engagement piece at a narrow side of the shank is smaller than the first length of the elastic engagement piece at a wide side of the shank, thereby increasing an elastic modulus of each the elastic engagement piece along the axial direction to beneficially resist vibrational loosening.
According to another embodiment of the present invention there is provided a tool holder apparatus, wherein: each the elastic engagement piece is sloped toward the narrow side of the shank relative to a plane perpendicular to the central axis, and each the ring-shaped groove is oriented toward the narrow side of the shank relative to a plane perpendicular to the central axis, whereby the plurality of elastic engagement pieces resist removal of the shank from the tapered hole.
According to another embodiment of the present invention there is provided a tool holder apparatus, wherein: each the elastic engagement piece extends from the shank in a plane perpendicular to the central axis.
According to another embodiment of the present invention there is provided a tool holder apparatus, wherein: each elastic engagement piece is sloped toward the wide side of the shank relative to a plane perpendicular to the central axis, and each the ring-shaped groove is oriented toward the wide side of the shank relative to a plane perpendicular to the central axis, whereby the plurality of elastic engagement pieces enables easy removal after use while ensuring tight attachment to the main shaft.
According to another embodiment of the present invention there is provided a tool holder apparatus, further comprising: at least one elastic flange on the shank, the elastic flange extending from the shank and abutting an outer end surface of the main shaft during the insertion, the elastic flange abutting the outer end surface along a continuous radius and providing an increased stability between the shank and the main shaft during the insertion and the use, and the elastic flange elastically deforming away from the outer end surface shank during the insertion, thereby urging the shank out of the tapered hole during a removal.
According to another embodiment of the present invention there is provided a tool holder apparatus, wherein: the at least one elastic flange having a ring shape with a circular abutting piece at an outer diameter, a ring-shaped groove on the elastic flange at a radially inward position opposite the circular abutting piece, and a ring-shaped sloped groove on the elastic flange at a radially outward position opposite the ring-shaped groove, whereby the ring-shaped groove and the ring-shaped sloped groove assist the elastic flange in elastically urging the tool holder from the tapered hole during the removal.
According to another embodiment of the present invention there is provided a tool holder apparatus, wherein: the plurality of elastic engagement pieces are a plurality of collar-shaped members individually secured to an outer perimeter section of the shank.
According to another embodiment of the present invention there is provided a tool holder apparatus, wherein: the plurality of elastic engagement pieces are a plurality of flat springs mounted on an outer perimeter section of the shank, and the plurality of flat springs being between the shank and the tapered hole.
According to another embodiment of the present invention there is provided a tool holder apparatus, further comprising: at least a first groove on the shank, the at least first groove on an outer diameter of the shank, and at least a first key extending from the tapered hole and engaging the first groove on the shank and allowing easy torque transfer from the main shaft to the tool support section during the use while enabling the insertion.
According to another embodiment of the present invention there is provided a tool holder apparatus, wherein: a cross-section of the tapered hole and the shank along a plane perpendicular to the center axis being a non-circular shape, the tapered hole having a non-circular inner surface parallel to a non-circular outer surface of the shank, at least a first groove in the plurality of elastic engagement pieces, and at least a first projection extending from the shank and engaging the non-circular inner surface during the use, whereby the at least first projection engages the non-circular inner surface and prevents rotation of the tool holder relative to the main shaft during the use.
According to another embodiment of the present invention there is provided a tool holder apparatus, wherein the plurality of ring-shaped grooves have smooth radius contours, thereby minimizing elastic stress concentration.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.